Effect of Al(III) and Sulfate Ion on Flocculation Kinetics

Abstract

The kinetics of orthokinetic flocculation of a dilute monodispersed polystyrene suspension initially coated with aluminum hydrolysis products (AHP) and destabilized by sulfate ion addition can be described by a modified Saffman and Turner kinetic model. The modifications include: (1) substituting for the collision efficiency parameter an expression which includes the effect of hydrodynamic forces, as well as double‐layer repulsion and van der Waals attraction on the particleparticle interaction; (2) relating the volume fraction, ϕ, to the amount of adsorbed AHP; and (3) assuming that the initially unadsorbed AHPs are deposited on the coated particle as a function of time after sulfate ion addition. The rate of uptake of AHP is assumed to be a function of hydrodynamic and surface chemical conditions; the AHPs are probably transported to the flocculating polystyrene particles as coagulating microcrystals or aggregating polymeric forms, and consequently ϕ increases with time.